Such disc brakes contain two levers of a brake caliper pivotally mounted at their lower end and two likewise pivotally mounted and opposing lining carriers with replaceable friction linings which are caused to be forced against a brake disc arranged on a driving or driven shaft during the braking operation. With these disc brakes, the pivotal plane of the opposing levers is parallel to the axis of rotation of the brake disc. A brake force generator in the form of an adjustable brake spring effects the closing of the brake during a braking operation via a lever linkage coupled to the free end of the brake caliper lever, the lever linkage being automatically compensated for wear at the friction lining. A releasing unit coupled to the same lever linkage generates the necessary force for overcoming the brake spring and thus for releasing the brake.
In comparison with drum brakes which are mainly used in the iron and steel industry in particular, disc brakes have substantial advantages.
Through the use of highly developed friction lining materials in conjunction with the shape of the lining and the favourable wear behaviour achieved by this, disc brakes have a very much longer service life than drum brakes. Another advantage of disc brakes is that the braking torque can be varied by the brake diameter without changing the brake mechanism whereas with drum brakes a brake drum of the appropriate diameter must be chosen to change the braking torque whereby a brake mechanism matched to the drum diameter is required at the same time.
By virtue of the indisputable advantage of disc brakes, drum brakes are being increasingly replaced by disc brakes in industrial installations of all kinds.
In the replacement of a drum brake by a disc brake in existing installations, one problem which exists is that on account of the limited space available between the drive motor and the gearing the overall dimensions of the disc brake in the direction of the axis of rotation of the brake disc may not be appreciably greater than the width of the brake drum of the drum brake originally fitted. With older crane installations, a further complication is that due to the incorporation of the release unit in the drive motor circuit a bulky electromagnetic release unit with a dc drive must be used.
With the generic disc brake as specified in U.S. Pat. No. 3,968,864 which is characterized by a compact design, disc springs are used as brake force generators whereby the two brake levers of the brake caliper are each driven by a disc spring assembly. However, experience has shown that disc springs are a risk factor for brakes with a high on/off frequency due to their limited service life. Furthermore, by virtue of their steep spring characteristic, they have a limited adjustment capability. But this adjustment capability of the brake springs is a desirable feature for taking account of the different application situations of the brake. Finally, due to its complicated mechanism, the known disc brake has a high fault liability and in the form described cannot be operated with the electromagnetic dc release unit usual in US drum brakes.